Gb Maguire

Effect of ammonia on the growth rate and oxygen consumption of juvenile greenlip abalone, Haliotis laevigata Donovan

Abstract Juvenile greenlip abalone, Haliotis laevigata , (mean whole weight 4.48±1.9 g, mean±s.d., n =953) were highly sensitive to ammonia as indicated by depressed growth rate and food consumption measured over 2–3 months in bioassay tanks. For growth rate expressed on a whole weight basis, the EC 5 and EC 50 values (5 and 50% growth reductions) were 0.041 mg FAN l −1 (Free Ammonia–Nitrogen) and 0.158 mg FAN l −1 , respectively. Shell growth rates declined over the entire experimental range (0.006–0.188 mg FAN l −1 ). At the end of the bioassay, groups of abalone were transferred to respiratory chambers. Oxygen consumption rate increased to a maximum of 188% of control values at 0.235 mg FAN l −1 and decreased slightly at the highest concentration of 0.418 mg FAN l −1 .

Acute and chronic toxicity of ammonia to juvenile Metapenaeus macleayi and Penaeus monodon and the influence of low dissolved-oxygen levels

Abstract Acute toxicity of ammonia was estimated as 96-h LC 50 values. For juvenile school prawns, Metapenaeus macleayi , and leader prawns, Penaeus monodon , these were 1.39 and 1.69 mg un-ionised ammonia, NH 3 -N/l (26.3 and 37.4 mg total ammonia-N/l), respectively. Reduced dissolved-oxygen (DO) levels significantly ( P P. monodon . Ninety percent of prawns held for 96 h at a DO level of 2.3 mg/l and an ammonia concentration of 1.60 mg NH 3 -N/l (33.5 mg total ammonia-N/l) died, whereas only 33.3% died at a DO level of 5.7 mg/l and a similar ammonia concentration of 1.63 mg NH 3 -N/l (33.9 mg total ammonia-N/l). The “maximum acceptable” level of ammonia was defined as that which reduced growth by 5% over 3 weeks. For M. macleayi and P. monodon these levels were 0.35 and 0.21 mg NH 3 -N/l (7.7 and 4.1 mg total ammonia-N/l), respectively.

Lethal levels of low dissolved oxygen and effects of short-term oxygen stress on subsequent growth of juvenile Penaeus monodon

Abstract The lethal level (96 h LC50) of dissolved oxygen (DO) for juvenile Penaeus monodon was estimated to be 0.9 mg O2 l−1 (95% confidence limits: 0.8, 1.0 mg O2 l−1). Other replicate groups of P. monodon were subjected to short-term, severe DO stress and then grown under conditions approaching DO saturation. The aim was to simulate the type of event which can occur in ponds when emergency aeration successfully raises DO after an oxygen crisis. Neither the duration (4, 8 or 12 h), nor the level (0.5-0.6 or 1.0–1.1 mg O2 l−1) of the DO stress significantly (P>0.05) reduced subsequent growth or food conversion efficiency at favourable DO levels over 21 days. Prawn pond managers should not need to reduce feeding levels or consider premature harvest after a single, short-term DO crisis when mass mortality is avoided. This is provided that other water quality variables do not reach critical levels during the crisis.

Low dissolved oxygen reduces growth rate and oxygen consumption rate of juvenile greenlip abalone, Haliotis laevigata Donovan

Juvenile greenlip abalone, Haliotis laevigata, (whole weight 10.8±3.0 g, mean±SD, n=603) were grown for 57–77 days in bioassay tanks at a range of dissolved oxygen (DO) concentrations (4.2–8.9 mg DO l−1; 55–117% oxygen saturation). Specific growth rate (SGR) was significantly affected by hypoxia whether measured on a length (P<0.01) or whole weight (P<0.001) basis. For growth expressed on a whole weight basis, the EC5 and EC50 values (5 and 50% reductions in growth rate) were 7.36 and 5.91 mg DO l−1 (96 and 77% saturation), respectively. Shell growth rates declined over the entire experimental range. At the end of the bioassay, groups of abalone were transferred to respiratory chambers. Oxygen consumption by juvenile greenlip abalone was significantly affected by the external oxygen concentration (P<0.01). The EC5 and EC50 values (5 and 50% reductions in respiration rate) were 6.16 and 5.19 mg DO l−1 (80 and 68% saturation), respectively. Oxygen consumption was estimated to be independent of external oxygen concentration in the range 6.25 mg–8.9 DO l−1 (81–117% oxygen saturation).

Effects of pH and salinity on survival, growth and osmoregulation in Penaeus monodon Fabricius

Abstract Critical levels of low pH for juvenile Penaeus monodon (4.2–5.5 g average weight), were determined using static bioassays with seawater acidified by using hydrochloric acid ( HCL ). The lethal pH (96 h LC 50 ) was 3.7 (95% confidence limits; 3.4 and 4.1 ) at a salinity of 32‰. The minimum acceptable pH, defined as that pH which reduced growth by 5% over 23 days, was estimated as 5.9 at a salinity of 30p. In comparison to a pH of 7.8, long-term (23 days) exposure to low pH (4.9) at 30‰ salinity also significantly decreased dry matter content of the prawns ( P P P P > 0.05) while the pH × salinity interaction was significant ( P P P P > 0.05). The estimation of lethal and minimum acceptable low pH values should assist prawn farmers with the management of acid ponds.

Effects of pond preparation and feeding rate on production of Penaeus monodon Fabricius, water quality, bacteria and benthos in model farming ponds

Abstract Fibreglass pools with sediment were used as model farming ponds to investigate the interactive effects of pond preparation and feeding rate on prawn production, water quality, bacterial dynamics, abundance of benthos and prawn feeding behaviour. Pools were either fertilised 1 month (prepared) or 2 days (unprepared) prior to stocking and either ‘high’ or ‘low’ feeding rates were used. The ‘high’ rate was 5.0% (range 4–8%) wet prawn biomass/day and was similar to that recommended for commercial farms. The ‘low’ rate was 2.5% (range 2–4%) wet prawn biomass/day. Juvenile Penaeus monodon (2.0–7.5 g) were stocked at 15 prawns/m 2 and were cultured for 71 days. With the exception of one prepared, high feeding-rate pool where mass mortality (> 80%) of prawns occurred following an interruption to aeration, prawn survival was high (> 86%) and was unaffected by preparation, feeding rate or their interaction. Pond preparation improved growth and biomass gain by about 20%. Growth was 4% higher with the higher feeding rate but biomass gain was not affected and, as food conversion ratio was much worse, use of the lower feeding rate offers considerable scope to reduce production costs, especially during cooler periods. There was no interaction in relation to growth between pond preparation and feeding rate. Meiofauna were more abundant, and prawns grew faster, in prepared pools than unprepared pools at the start of the experiment. However, changes in bacterial dynamics or meiofauna abundance over time did not explain reductions in prawn growth over time. In general, water quality was reduced in pools receiving the high feeding rate compared with low feeding rate pools. Other interactive effects of pond preparation and feeding rate on water quality, bacteria, benthos and prawn feeding behaviour are discussed.

Effect of photoperiod and light intensity on survival, development and cannibalism of larvae of the Australian giant crab Pseudocarcinus gigas (Lamarck)

Pseudocarcinus gigas larvae were reared to megalopa under two light intensities 2 and 500 . . lux in five photoperiod regimes 0, 6, 12, 18, and 24 h light . Survival was not significantly . affected by photoperiod or light intensity P) 0.05 , although other effects were observed which are discussed in relation to swimming activity and feeding. Larvae had shorter intermoult duration in treatments with longer photoperiods and brighter light with most rapid development to . . megalopa in the continuous light, 500 lux treatment 49.2 d . Size measured as telson width of stage 4 zoeas was affected by photoperiod with smallest zoeas in the continuously dark treatment, whereas all other treatments were similar. Cannibalism was strongly influenced by lighting with greater damage to the dorsal spine occurring with increasing photoperiod and also in dimmer 2 . lux treatments. Lowest incidence of cannibalism was observed in continuous darkness. Viability of larvae after metamorphosis to megalopa was variable and no treatment effect was observed although viability was lowest in the two continuous light treatments. Results of this trial indicate that continuous light or dark regimes should be avoided. Optimal light intensity for culture was less clear and is discussed in relation to intermoult duration and cannibalism. q 1998 Elsevier Science B.V. All rights reserved.

Effects of stocking density on production of Penaeus monodon Fabricius in model farming ponds

Sixteen 3.5-m diameter, 1.2-m high fibreglass pools with sediment were used as model prawn-farming ponds to investigate the effects of four stocking densities ( 5, 15, 25, and 40 prawns m−2) on prawn survival, growth and biomass gain, water quality, natural food resources, prawn feeding behaviour and economic return. Prawn survival was high ( >88%) and unaffected (P> 0.05) by density and there was a significant (P 0.05). Dissolved oxygen and concentration of algal pigments were affected by density (P < 0.001), although density-related effects on water quality did not explain reductions in prawn growth with increased density. The population density of macrobenthos, but niot of meiobenthos, within the sediment layer in each pool declined with increasing stocking density. However, the decline in growth of prawns at higher densities may have been due to decreased grazing activity as indicated by the number of stomachs containing neither natural nor supplementary feed.

The effect of different combinations of dietary calcium and phosphorus on the growth of juvenile Haliotis laevigata

Abstract A basal diet containing 0.45% Ca and 0.51% P was supplemented with 3, 2, 1 and 0% CaCO 3 both with and without 0.5% NaH 2 PO 4 . Diets were fed to replicate groups ( n = 4) of ten juvenile greenlip abalone ( Haliotis laevigata ) in 10 l flow through aquaria for 61 days after a 21 day acclimation period. Absolute and specific growth rates were calculated for both shell length (SL) and whole wet body weight (BW). Dietary Ca supplementation did not significantly affect growth ( P > 0.05), however the specific growth rate (BW) of animals fed diets supplemented with P was 7.9% higher than that of animals fed diets without P supplement ( P P > 0.05). Shell thickness was apparently unaffected by dietary Ca level. Mortality due to natural causes was not affected by diet ( P > 0.05); the range was 0–7.5% ( n = 8 treatments). The average feed conversion ratio (FCR; feed input per unit weight gain of wet abalone) for all diets was 1.19 ( r : 0.93–1.4) when uncorrected for uneaten diet, and 0.90 ( r : 0.80–0.96) when corrected. The apparent availability of CaCO 3 was 65.6%. These results suggest that abalone do not require high levels of Ca in their diet ( 3 is unnecessary, but P supplementation (>0.7% total P) can improve growth rates. The Ca:P ratio of feed is not important within the range assessed (0.72:1 to 2.68:1). Further research on the effect of greater P supplementation on growth rate and the treatment of plant ingredients to liberate P bound by phytate is required.

A study of the optimum stocking density and feed rate for school prawns Metapenaeus macleayi (Haswell) in some Australian brackish water farming ponds

Abstract A stocking density experiment was conducted in 18 experimental enclosures within a single 0.11 ha pond. As stocking density increased in the range 6.1–21.2 prawns/m 2 , school prawn growth declined while survival rate was unaffected and total harvest (final biomass) increased. A simple economic analysis indicated that the optimum stocking density for juvenile school prawns was 19.1 prawns/m 2 . In a similar experiment the effects of feeding school prawns with a pelleted diet at a range of supplementary feed rates (0–12.5% of prawn biomass/day) were investigated. The optimum feed rate in terms of growth was approximately 5% of biomass/day. However the optimum feed rate, in terms of the economic return index used, varied depending on the estimated cost of the diet.